Dura ace 7900 cassette gear ratios ??

stigma
stigma Posts: 51
edited October 2010 in Road buying advice
The Shimano Dura Ace CS-7900 cassette provides 8 different ratios to choose from -- 11-21, 11-23, 11-25, 11-27, 11-28, 12-23, 12-25, and 12-27.

Can someone please enlighten me on the differences and use for these different options?
Which one is the best use for say, hill climbing, "regular use" and TT ??

Comments

  • fleshtuxedo
    fleshtuxedo Posts: 1,853
    Hi, er, Stigma. Depends where you live, what your fitness level is and what chainrings you're using (ie standard 39/53 or compact) - if you add this to the thread I'm sure you'll get some advice.
  • There are maybe too many variables to give a meaningful answer, and I guess it also matters somewhat if you run a compact or standard chainset.
  • stigma
    stigma Posts: 51
    I run a compact 53/39
  • amaferanga
    amaferanga Posts: 6,789
    53/39 is a standard double, not a compact.

    If you live somewhere that isn't too hilly or you're a good climber you should be okay with a 11-23.
    More problems but still living....
  • Bar Shaker
    Bar Shaker Posts: 2,313
    53/39 is a standard crankset.

    TT courses are normally flat so you want close ratios and would chose a 12-23 or 11-23 maybe an 11-21. Normal terrain would require an 11 or 12-25 or 27. Very hilly areas may need a bigger range than from 25, possibly 27 or bigger.

    Running a standard crankset a low 12 and high 25 would be a good starting point.
    Boardman Elite SLR 9.2S
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  • northpole
    northpole Posts: 1,499
    If you are running a standard chainset and you are not club level fit and you want to tackle some fairly challenging hills, my advice would be:
    1. Change immediately to a compact chainset
    2. If you take option 1. above, I would suggest a cassette with 11-25 or 12-27 - really depends on your hill climbing capability. 11-27 and 11-28 I suspect would be too wide a range and create several times when you'd feel like you were in the wrong gear.
    3. If you are sticking with a standard chainset, you should get a cassette with a minimum large sprocket of 27.

    Best way to narrow the selection criteria is to go on a decent ride on your current set up and objectively analyse how well you cope with long drags of hills - IF that is the terrain you will be tackling. Particularly interesting is to climb the hill towards the end of your ride, when energy levels may not be tip top!!

    For every day use, a 12-25 is hard to beat.

    For flatter riding ie no major climbs, a 12-23 offers a really close set of ratios which you can whiz through and always find the sweet spot.

    Hope that is of some help.

    Peter